esp32 spi 64kBytes transaction and dma question

[brebisson]

Hello,

I am using a TTGO board with a LCD, no PSRAM, and I want to use the SPI to send a full LCD frame (64KBytes) to the LCD.

I am using the spi API described here:
https://docs.espressif.com/projects/esp ... on-example

The data is 64KB frame buffer which is a global variable (in DRAM I assume as there is nothing else on this chip).

Can I create a single transaction to send these 64KB at once?
Will it use the DMA to send the data (the spi_bus_initialize call did specify SPI_DMA_CH_AUTO).

Thanks,
Cyrille

[ESP_Sprite]

Yes you can and yes it will. Just make sure to set max_transfer_sz in your spi bus config accordingly.

[brebisson]

hello,

What does the max_transfer_sz parameter do exactly?

does it mean that the driver will allocate a buffer of that size? or will it use my buffer?

Cyrille

[ESP_Sprite]

What does the max_transfer_sz parameter do exactly?

does it mean that the driver will allocate a buffer of that size? or will it use my buffer?

It will make sure enough DMA descriptors are allocated so your buffer can be DMA'ed out successfully.